[LottyLouis]

So - I've been digging down my new (sadly neglected) allotment and planting up as I prepare each patch. I've been regularly coming across large ant colonies - they swarm over the earth as I dig it. I've been ignoring it planting loads of veggies - all are doing well.
I've just got to the end of the plot and have found several more 'anty areas' (red ones and black ones) and it's got me thinking. I know our soil should be teeming with wildlife - but are the ants going to harm crops in any way?   

[Dai]

I feel your pain as I have the same problem, last year I had the odd potato plant die off and when digging them up I found ants underneath them which I'm blaming for their demise.
usually when you disturb the nest they move into another area. I'm guessing that they are good for soil aeration but if they nest too close to the roots of a plant they will be detrimental to it.

One thing I've been meaning to try is mixing half and half baking powder with castor sugar made into a paste with some water and putting it down by the nest. The ants will take this back to the colony and it will kill them off (or so I've read)

Another thing you could try is borax powder.

[LottyLouis]

Hmmm...I was hoping we could all rub along together. 

[mjg000]

I have read - and think I believe it - that the ants are actively encouraging the blackfly up the Broad Beans because they enjoy the sugary sap which is then secreted.  I know that I have definitely seen lots of ants near the beans when they are attacked by blackfly.  I rarely get round to dealing with the nests but think I might next year.

[LottyLouis]

Yes, ants and blackfly certainly go together. When I was looking for blackfly on my broad beans (like I had to seek them out!) all I had to do was to follow the ants. It was always the black ants - not the red ones. I read somewhere that the ants 'farm' the blackfly, like they do aphids. I have certainly watched ants pick up blackfly and scurry off with them when I was spraying (soap - not bug-killer). I also understand that the ants will defend the blackfly against the ladybirds - so it's all terribly complicated.
My question though concerns the section of allotment that has just been dug and not yet planted. LOADSA ants. Will they harm anything that I plant there? There is certainly no sign of damage at the other end of the lotty where there are new plants and lots of ants - so maybe we can all live together. 

[LotuSeed]

Ants definitely "farm" other insects. They milk them for honeydew (that's how I was able to spot a scale bug on my blackberry bush). I've had quite a few nests in one of my potato beds but I just leave them be. I haven't noticed them causing any harm to my plants.  If they were ruining stuff, I'd probably just try to relocate them to somewhere else in the yard.

[grinling]

If farming the aphids,put jam above the aphids and ants eat that and then the aphids.
Do not plant directly into a nest site as I found they kill the seedlings, has loads of spares.
The ones in the polytunnel will swarm shortly!!!!
I have used oil of cloves in a watering can which has helped and smells nice to. I don't like to poison esp since we had a green woodpecker which only eats ants turn up a couple of years ago.
I have also seen ants looking after wasps eggs as if they were their own.

[Salmo]

The ants will do more good than harm. Once you have disturbed them with cultivations their numbers should decrease. In a dry season they can kill plants but generally not.

They feed on the honeydew secreted by aphids, black or green. Ants carry juvenile aphids higher up the plants so that they can feed on nice young growth and produce more honeydew. They must be admired for their enterprise.

There are many other predators besides ladybirds and their larvae that feed on aphids. Just watch a big colony of black aphids, perhaps on a dock or thistle. There will almost certainly be hoverflies around it. They lay their eggs amongst the aphids. You can often see the orange maggots within the colony.

[LotuSeed]

They are fascinating to watch.

[Dai]

Well after reading all that I think I'll leave them be aswell, especially since I've heard a woodpecker in the woods opposite my plot.

[strangerachael]

Yes I have had the odd plant die off and found an ants nest underneath, it's usually just one or two per row. The ants are definitely worse in a dry year.